FIG. 6 is partial cross section of a conventional gas turbine engine generally indicated by reference numeral 100, showing a connection between a turbine disk generally indicated by reference numeral 101 and a blade member generally indicated by reference numeral 102. As shown, the turbine disk 101 has a circumferential surface 103 extending in a rotational direction 104 about a rotational axis of the engine 100 (not shown). The circumferential surface 103 has a plurality of grooves 105 defined therein at regular intervals in the rotational direction 104. The grooves 105 are extended in a direction substantially parallel to the rotational axis.
For example, the groove 105 has a cross section defined by a pair of opposed side walls 106 and a bottom wall 107 connecting the side walls 106. In particular, the side walls 106 are corrugated symmetrically to have two inwardly facing portions 108a and 108b diverging from the circumferential surface 103 toward the rotational axis. The blade member 102 has a blade 109 and a root 110 integrally formed therewith. The root 110 has a configuration which is substantially complementary to that of the groove 105, so that the blade member 102 is assembled on the turbine disk 101 with its root 110 fitted or engaged within the groove 105.
This arrangement needs small gaps 111 or clearance between the groove walls and the root walls in order to facilitate the assembling or sliding engagement of the root 110 into the groove 105, which disadvantageously induces an unwanted leakage of cooling medium or air 112 supplied through air channels 113 and 114 defined in the turbine disk 101 and blade member 102, respectively, for cooling the blade 109 and thereby increasing a heat durability of the blade 109 against high temperature combustion gas. In the illustrated arrangement, the outlet opening of the channel 113 in the turbine disk 101 is opened at a bottom wall portion 115 of the groove 105 and the inlet opening of the channel 114 in the blade member 102 is opened at an opposing bottom wall portion 116 of the root 110 so that the cooling air 112 supplied from a source (not shown) is delivered through the channels 113 and 114 into a cooling chamber or passages defined in the blade 109 (not shown) for its cooling. During the air supply, the cooling air 112 disadvantageously flows in part into the gaps 111 to be eventually wasted into the turbine chamber 117, which in turn degrades the cooling efficiency of the blade 109.
One technique which may be used for solving this problem is disclosed in the U.S. Pat. No. 5,160,243. According to this technique, a metallic reinforced shim is mounted in the gap between the turbine disk and the blade member to cover the pair of diverging side walls and the bottom wall of the root so that the portions of the shim covering the side walls are tightly nipped by the side walls of the root and the opposing side walls of the groove due to centrifugal force caused by the rotations of the turbine disk.
This technique may also be applied for sealing the gaps 111 around the opposed openings of the cooling air channels 113 and 114. For example, as shown in FIG. 6, a plate-like shim 118 with an aperture 119 may be provided in the gap 111 between the opposed bottom walls 115 and 116 of the turbine disk 101 and the root 109 so that the opposed openings of the channels 112 and 113 are fluidly communicated through the aperture 116, allowing the cooling air 112 to flow from one channel 113 through the aperture 119 into the other channel 114.
This arrangement, however, has drawbacks. For example, if a thickness of the shim 118 is designed to be smaller in order to facilitate the insertion or positioning of the shim 118 into the gap 111, the shim 118 is firmly forced on the bottom wall 116 of the root 110 due to the centrifugal force caused by the rotations of the turbine disk 101 to cause another gap (not shown) between bottom wall 115 of the groove 105 and the opposed outer surface (i.e., lower surface in FIG. 6) of the shim 118, still allowing the leakage of the cooling air 112. If on the other hand the thickness of the shim 118 is designed to be substantially the same as or slightly larger than the gap 111, the assembling or insertion of the shim 118 will become significantly difficult. Also, if the shim is inserted forcedly, it may buckle within the gap to cause a misalignment of the aperture, which results in that the channels are in part blocked by the shim.
Therefore, according to the above-described techniques, in order to enhance the cooling efficiency and the assembling, it is necessary to machine the shim with a high degree of precision, which results in a drastic increase of the manufacturing cost of the shim. Also, the size of the gap may vary significantly due to the dimensional tolerances of the turbine disk and the blade member, so that the high precision machining of the shim may be of useless. Further, a fixing means may also be needed to hold the shim in position in the gap.